mrb's blog

Looking at 6-, 8-, and 12-core Processors

Keywords: amd cpu hardware intel processor

As someone doing research in cryptographic brute force attacks, which are embarrasingly parallel workloads, I keep an interested eye on the latest advances in multi-core processors. I like to look at raw computational abilities and prices, and always do all sorts of quick estimations in my head to get an idea of what is possible at what cost. The AMD Magny-Cours and Intel Westmere families of processors recently brought to the market a significant number of new models with 6 cores or more. I will look at them in this post and explain why AMD provides more value per dollar.

First of all, I like to use the following official price lists as quick references of the current offerings. I like the fact the URLs are short enough they can be memorized:

I also included links to online databases maintained by AMD and Intel to check the technical features supported by a given processor model (wattage, max DDR3 frequency, or any feature that Intel is notoriously not consistent in enabling on all processors of a given family: Turbo Boost, etc). Notice how these databases are easy to use and practical, unlike the massive mazes of non-technical information provided by the corporate websites of both vendors. Crypto workloads are often purely CPU-bound and scale linearly with the frequency clock and with the number of cores. With these price lists, one can see why AMD is often touted as providing more performance per dollar:

  • For $200 you can get a 6-core Phenom II X6 1055T 2.8GHz. Intel has no 6-core or more processor at this price point. This Phenom with a Thuban core is actually similar to Istanbul and not Magny-Cours.
  • For $300 you can get an 8-core Opteron 6128 2.0GHz, or a 6-core Phenom II X6 1090T 3.2GHz. Intel has no 6-core or more processor at this price point.
  • For $800 you can get a 12-core Opteron 6168 1.9GHz, or an 8-core Opteron 6136 2.4GHz. Intel still has no 6-core or more processor at this price point.
  • For $1000 you can finally buy Intel's cheapest 6-core processors: Core i7-980X 3.33GHZ, or Xeon W3680 3.33GHz, or Xeon X5650 2.66GHz, or Xeon L5640 2.26GHz. At this price point AMD sells the 12-core Opteron 6172 2.1GHz, or 6-core Opteron 2439 SE 2.8GHz (latter not Magny-Cours, but included for reference).
  • For $2500 you can buy Intel's cheapest 8-core processor: Xeon X6550 2.0GHz. Or you can buy two 12-core Opteron 6168 1.9GHz for $1500 (2*$750) for slightly slower cores but a total of 24 of them instead of 8, and have a remaining unspent $1000 to cover the extra operating costs (power, cooling) for the next 5 to 15 years. That is, assuming 50 to 150 extra Watts for each X6550 replaced with a pair of 6168, an average PUE of 1.5, 24/7 operation, and $.10/kWh, which gives 1000/(.150*1.5*24*365*.1) = 5 years; or 1000/(.050*1.5*24*365*.1) = 15 years. Note that the 50 to 150 extra Watts is my wide conservative estimate range; a naive calculation would indicates 2*80-130 = 30 extra Watts (130W TDP X6550 replaced with two 80W ACP 6168) but this number does not account for the extra gear needed to support the 2nd processor (motherboard/RAM/fans/etc) and for the fact that TDP is not directly comparable to ACP.

Note that by ignoring processors with 4 or fewer cores, the above list may not reflect it, but Intel sometimes can offer a value per dollar very close or superior to AMD for 2 reasons: higher clock frequency, and a generally higher IPC ratio (Instruction Per Clock). For example when comparing the 2 similarly priced 6-core i7-980X 3.33GHz and 12-core 6172 2.1GHz, assuming a workload having a 25% IPC advantage on the Westmere microarchitecture compared to the Magny-Cours microarchitecture (a pretty common number I have personally seen with different workloads), a quick estimate shows that Intel, despite having only half as many cores, can in this example provide roughly the same performance as AMD for a purely CPU-bound and parallel workload:

  • Intel: 6 (cores) * 3.33 (GHz) * 1.25 (IPC advantage) = 25 "core.performance"
  • AMD: 12 (cores) * 2.1 (GHz) = 25.2 "core.performance"

In conclusion, 6-, 8-, and 12-core processors represent a small fraction of the processor market today. It will take a while for these products to have an impact on AMD's or Intel's success. However this fraction of the market will only grow, and what the above numbers reveal is that AMD is very well-placed to compete aggressively with their prices and value. It is no surprise for example that tier-1 vendor HP recently announced their entire family of G7 servers will be based on AMD Magny-Cours. If you are buying a 1-socket workstation or building a 1000+ socket cluster to run crypto workloads or generally CPU-bound workloads, AMD is probably the better choice as of today, unless Intel dramatically cut prices across the board. Realize that you may even be able to fit twice as many Magny-Cours processors in a given physical rack space compared to Westmere processors because the overall lower Magny-Cours power consumption allows four G34 sockets in 1U as this SuperMicro server demonstrates. Westmere just cannot do this. "Abolishing the 4P tax" —as AMD said it— by pricing the Magny-Cours 6100 series the same for 2-socket and 4-socket (and more) configurations was an excellent strategic move IMHO. I am impatient to see how the soon-to-be-announced Lisbon 4100 series will be priced.